THE LATE QUATERNARY INITIATION AND PALEOECOLOGICAL HISTORY OF MID-ATLANTIC WETLANDS

In the mid-Atlantic US, few freshwater wetlands and peatlands exist today south of the extent of glacial ice maximum. However, recent work on valley bottoms in Pennsylvania and Maryland has revealed extensive Holocene floodplain marshes and fens, now buried by anthropogenic “legacy” sediments. We hypothesize that these buried organic-rich wetland sediments capture the initial stages of extensive peatland development throughout the periglacial mid-Atlantic during the Early Holocene. Here, we present paleoecological research into the initiation, extent, and history of late Pleistocene to Holocene freshwater wetlands in the Mid-Atlantic province. We investigated both surviving and buried peat-accumulating wetlands in Pennsylvania and Maryland using radiocarbon dated loss-on-ignition and macrofossil stratigraphies. In the Piedmont, radiocarbon ages of basal organic accumulation at Little Conestoga Creek, PA was 8.6 ka and at Great Marsh, PA was time transgressive between 11.5 and 9.4 ka. We compare those initiation dates to organic-rich wetlands throughout the mid-Atlantic by synthesizing basal radiocarbon ages of other regional wetlands and peatlands, including high Appalachian peatlands, saltwater marshes, and buried off-shore peats on the east coast. Preliminary analysis shows the rapid initiation of wetlands in the MidAtlantic and periglacial Appalachians between 12 and 8 ka. However, in many cases, rates of organic matter accumulation slowed substantially around 6-7,000 years ago, during a time of high temperatures at mid-latitudes. Taken together, we suggest that wetlands rapidly expanded throughout the mid-Atlantic during the early Holocene and represent an analogue for the modern "greening" of artic environments.